The field of the invention is permanent magnet motors, and particularly, motors with high power density.
The power rating of a motor is primarily a function of its size. Larger motors provide more air gap area over which the magnetic fields can interact to produce a higher torque. In a conventional radial-gap motor the rotor is generally cylindrical in shape and permanent magnets are mounted around its outer surface to face radially outward to a surrounding annular air gap. The stationary stator winds are disposed around the annular air gap and produce rotating magnetic fields that interact with the fields produced by the rotor magnets to produce a torque which rotates the rotor. Examples of such permanent magnet motors are described in U.S. Pat. Nos. 4,625,135; 4,549,341; 5,280,209; and 4,117,360.
Axial-gap permanent magnet motors have a rotor in which magnets are mounted to one or both ends of the rotor and face in the axial direction. The air gap is formed at one or both ends of the rotor and the stator windings produce rotating fields that are projected axially across the air gap to interact with the magnet fields. Examples of such axial-gap motors are disclosed in U.S. Pat. Nos. 4,996,457; 5,117,141; 5,619,087 and 4,578,610.
None of these prior motors are optimized for maximum power density.